Field of the Invention
The present disclosure relates to a touch sensing system, and more particularly, to a touch sensing system capable of performing a touch input using an active stylus pen.
Discussion of the Related Art
User interface (UI) is configured so that users are able to communicate with various electronic devices and thus can easily and comfortably control the electronic devices as they desire. Examples of the user interface include a keypad, a keyboard, a mouse, an on-screen display (OSD), and a remote controller having an infrared communication function or a radio frequency (RF) communication function. User interface technology has continuously expanded to increase user's sensibility and handling convenience. The user interface has been recently developed to include touch UI, voice recognition UI, 3D UI, etc.
A touch UI has been necessarily adopted to portable information appliances. The touch UI is implemented by forming a touch screen on the screen of a display device. The touch screen may be implemented as a capacitive touch screen. The touch screen having capacitive touch sensors senses changes (i.e., changes in charges of the touch sensor) in a capacitance resulting from an input of a touch driving signal when a user touches (or approaches) the touch sensor with his or her finger or a conductive material, and thus detects a touch input.
A stylus pen has been recently used as a human interface device (HID) in smart phones, smart books, and the like. The stylus pen is advantageous to perform more detailed inputs than fingers. The stylus pen includes a passive stylus pen and an active stylus pen. It is difficult for the passive stylus pen to detect a touch location of a touch screen contacting the passive stylus pen because of a small change in a capacitance at the touch location. Compared with the passive stylus pen, it is easier for the active stylus pen to detect a touch location of the touch screen contacting the active stylus pen because the active stylus pen generates a pen driving signal and outputs the pen driving signal to the touch location. Hence, the development of the active stylus pen has been focused.
In a related art touch sensing system, an active stylus pen transferred additional information (for example, pen pressure information) of the active stylus pen separately from a pen driving signal to a touch integrated circuit (IC), so as to implement various convenient functions. To this end, the related art active stylus pen individually transferred the pen driving signal and the additional pen information to the touch IC through a modulation method using a sine wave of a high frequency (for example, several MHz to several tens of MHz). The touch IC dividedly processed the pen driving signal and the additional pen information using a bandpass filter, a detection circuit, etc. The pen driving signal and the additional pen information had a frequency much higher than a touch driving signal for driving a touch screen.
Because the related art touch sensing system has to add a complex processing circuit for dividing the pen driving signal and the additional pen information to the touch IC, the size and the manufacturing cost of the touch IC increased.
Furthermore, the related art touch sensing system may be applied only to an add-on touch screen and cannot be applied to an in-cell touch screen. The add-on touch screen uses a touch screen formation method for attaching a touch screen to a display panel, and the in-cell touch screen uses a touch screen formation method for embedding touch sensors of a touch screen in a pixel array of a display panel.
Because touch sensors of the in-cell touch screen are coupled with pixel signal lines through a parasitic capacitance, an RC delay of the in-cell touch screen is greater than an RC delay of the add-on touch screen. Thus, it is difficult for the in-cell touch screen to accurately transfer the pen driving signal and the additional pen information of the high frequencies to the touch IC as in the related art touch sensing system because of lack of RC time.